1. Field of the Invention
The present invention relates to an extruder used to produce extrudates from a metal such as aluminum.
2. Related Art Statement
The prior art extruders for extruding aluminum or the like extrusile metal generally comprise an extrusion die giving a desired shape to the extrudates and a material passage feeding the metal to the die. An extrusion pressure is applied to the softened extrusile metal that is advancing in the passage towards the die, so that the extrudates of the desired shape are produced.
The present applicant has proposed, in its Japanese Patent Applications Nos. Hei.4-339997 and Hei.5-13318, a novel apparatus for continuously extruding a wire-shaped or rod-shaped raw material. However, those previous applications have neither been published yet, nor made known to the public.
As is shown in FIG. 7, this apparatus comprises a die 103 and a container 102 disposed in rear of the die and having a heater 101. The apparatus further comprises a material feeder 104 in rear of the container 102 so as to force the raw material into the container. The wire-shaped or rod-shaped material `W` of a small diameter will be urged into a passage 102a in the container 102, continuously at room temperature. Thus the extrusion pressure in the passage 102a remains at a proper level. This pressure will force an extrusile material through the die 103 to give an extrudate `E` of a desired profile, wherein the heater 101 previously heats and softens the material within the container 102.
Operation of such a continuous extruding apparatus is however not necessarily perfect in that, depending on the profile of extrudates, the feeder 104 possibly fails to apply a sufficient pressure to the extrusile material `M` in the passage 102a.
This problem is not inherent only in the apparatus shown in FIG. 7, but may also occur in the prior art billet extruders wherein a metal billet in the container is forced towards a die. In other words, such a problem will occur in common in a variety of the extruders that comprise a die and a material feed passage in communication therewith.
It is another problem in the extruders exemplified in FIG. 7 that many factors sometimes cause an uneven temperature distribution in the extrusile material within the passage. In such an event, the extrusile material will soften to a variable degree. If a material not heated to completely soften is fed to the die, then an undesirably heavy load charged thereto will break it early.
The apparatus shown in FIG. 7 is designed to continuously force the wire-shaped or rod-shaped raw material into the passage 102a in the container 102. Inaccurate control of the heater 101 in this apparatus will result in an insufficient heating of the material `W` that is being forced into the passage 102a. This material `W` not completely softened is likely to break the die 103.
It is also noted that the extrusile material `M` must be in its properly softened state in the die 103 so as to ensure a good metal flow therethrough. Thus, the material `M` should be heated to a predetermined temperature before entering the die 103. The extruder in FIG. 7 employs the heater 101 to heat the material `M` while it is moving forward within the passage 102a. The heater 101 playing the most important role to heat the material will however increase thermal energy consumption and thus raise manufacture cost to a disadvantageous extent.
The same problem will be inherent in the billet extrusion system, because much energy will be consumed to heat the billet.